Encrypted Radio Transmission: What is & What is Not Safe

There are several ways to encrypt radio transmissions.

Encryption algorithms allow users to change the data appearing in a signal to prevent eavesdropping or jamming. This is done by both altering the characteristics of the transmitted data and also changing the order in which it appears.

Many cryptographic systems, such as Advanced Encryption Standard (AES), Inherently Secure Data Transmission System (IS-1304), One Time Pad (OTP), Rivest Cipher 4 (RC4) and more use this concept of altering data properties, but not necessarily its distribution in time, when encoding audio data.

Most Baofeng Radios are not encrypted out of the box. You would have to make modifications to the unit in order to encrypt your transmission. 

Encoding a voice signal can be accomplished in a number of different ways.

One method is using a vocoder, which uses a set of known speech synthesis frequencies to encode the analog information in a digital format. Vocoders can operate in either an analog or digital mode and are used to modulate carriers with voice signals.

A vocoder typically consists of two subsystems: the front end and the back end.

The front end has an excitation signal that can be a function of either a codebook or random noise samples. This is then passed through a filter where its spectral characteristics are altered according to the outgoing speech's frequency content.

The output from this stage is fed through another filter whose output becomes the input for the back-end analysis section. Here, various parameters such as pitch period, voicing decision, etc., are derived from the incoming signal, which are then encoded and made available for transmission.

Note that the modulator front end can produce signals more efficiently than a simple encoding of speech samples; therefore, vocoders are more efficient than audio compression algorithms (such as MP3 or Vorbis) at transmitting audio over bandwidth-constrained connections.

One common example is Frequency Shift Keying (FSK).  This technique simply shifts the frequency of the radio carrier up or down to correspond with 1's or 0's, respectively.

For example, if you have a signal on 146.520 MHz, it might shift this by +1 kHz to 147.520 MHz when sending a "1" and shift it by -1 kHz to 146.520 MHz for a "0". This is actually the simplest form of FSK.  The main drawback with this type of modulation is that it can interfere with other users on your same frequency.

A new method under development will send your voice using a series of dots and dashes like Morse code, but in this case the dots and dashes stand for complex waveforms rather than simple tones.  

The main advantage of this method is that it doesn't interfere with existing license-free systems at all, so there's no risk of jamming frequencies needed for fire or ambulance communications.

Decoding encrypted radio signals does not require much more hardware than what you need to receive regular audio transmissions; however, it does require significantly more processing power than simply listening to audio.  

To decode encrypted transmissions, you'll need a software defined radio (SDR) device.

The SDR will include an RF front end for receiving the transmission (and possibly transmitting as well), an ADC (Analog to Digital Converter) to digitize it, and finally some sort of computer with enough CPU power to run the decoding algorithm.

There are many different types of voice encryption algorithms; however, only a few are common enough to be worth mentioning here.  One is called FH-AES128c, which uses 128 bit AES in counter mode with 128 bit key update every 40 ms using 32 bit incrementing counters and 128 bit keystream.  

An older voice encryption method that is still in use today is called FH-E9 (E9 stands for Enhanced 9). This uses a very long, complex 40 byte key and an even longer table to pre-compute the product of two encryption key schedules.  The table used contains 2048 bytes of data, but because it's so large, AES128c is typically used instead.

Finally, we have the old-time tested Morse code! An example of this can be found here. This is the oldest radio communications there is.

This is where it gets tricky. It is legal to encrypt your radios but there are issues with using encrypted messages that can be disallowed by law enforcement or the military.

Enabling encryption on your radio does not make the message unreadable to anyone within range of receiving it, especially if they use a compatible type of radio.

The reason for this is because the radios are all using the same frequency. The only way someone cannot read your transmissions is if they do not have a radio that can either decode or encrypt what you are saying.

There are radios that offer preset encrypted channels. 

Encryption, as far as ham radio is concerned, falls under the same set of rules as ham radio transmissions in general.

The only thing different is the length of time you are allowed to encrypt your messages.

According to federal code, anyone using an amateur radio must accept incoming unencrypted messages.

But you can encrypt outgoing messages for a maximum of 72 hours after which point they must be sent out unencrypted or not at all.

Encrypted hams are considered to be just like any other ham with one exception: encryption counts against your duty cycle because it takes up more time than standard transmissions do.

This means that even if it is allowed according to federal laws but overused and slows down response times or prevents proper communication, then there might be consequences - especially when lives are at stake.

DMR is digital mobile radio. And yes, it is encrypted with most available radios also allowing you to turn the encryption feature off.

As far as doing so is concerned - there are specific times wherein it might not be wise to do so considering that DMR has open slots which anyone can monitor.

But for those who cannot use unencrypted transmissions, they can use VOX mode or push-to-talk buttons just like traditional analog radios.

There are different kinds of encryption available for users who want their information to remain private.

One type is called "data encryption" and it only scrambles the data within your transmission. Your carrier still knows where you are sending it, how much data you've sent out, etcetera.

This means that your identity can be traced even if there is no way to decrypt your messages … which happens often with most commercial services because most governments have an agreement with these companies.

Another kind of encryption is called "data privacy". Data privacy encrypts all of your outgoing messages so that not even your service provider can read them - but they cannot know who you are sending messages too or what the size of the message being sent is.

A trunked frequency is a group of frequencies that are grouped together and used to allow multiple voice or data transmissions at one time.

Trunking allows the groups to transition seamlessly from transmitted message to transmitted message with no lag in between. This means that it can accommodate more users without them having to take turns transmitting.

It is legal to listen to Police Radios on a scanner but there are regulations when it comes to spying on private conversations or police radio communications. In some states it is illegal to listen to the Police scanner

According to federal law, you cannot use your radio in a way that will intercept any conversation which does not want you to hear their transmissions - even if they happen upon the same channel as yours currently is. A Law Enforcement agency channel is typically Channel 9 

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This can be considered illegal eavesdropping has gone so far as some states have prosecuted people for doing so.

Some two-way radios are encrypted but they need to have an encryption switch in order for them to work.

It is most useful when people who are communicating on different radio frequencies than each other want to keep their transmissions secret from others with the same type of two-way radio.

Citizen's Band radios are not encryptable because their use was intended for civilian purposes only - which means that there were never any plans for them to be used by law enforcement or emergency personnel.

Their line of sight capabilities also make it difficult for them to be controlled properly by someone in charge even if they were able to encrypt their messages.

FRS (Family Radio Service) radios are not encrypted and transmit for civilian use.

GMRS radios service are not encrypted for civilian use as service was developed to be used by civilians (for recreation purposes).

Marine radios are usually set up to communicate directly with satellites or other vessels so encryption is unnecessary - but they can also be used for VHF transmissions once on land. These too are unencrypted.

Most ham radio services do allow their users to encrypt their transmissions... especially when using long-range communications technology. Encrypting is possible with Ham Radios by offering encryption keys. 

A lot of them also have data privacy or voice privacy which scrambles all outgoing messages so that it cannot be intercepted by anybody else who might be trying to listen in.

As a general rule of thumb, walkie talkie technology is mostly used for recreation purposes. There are some units that will allow users to encrypt their messages however - there are very few walkie talkies that have a function to encrypt a message.

Most commercially sold encrypted radios are for professional use - but there is a chance that they might be available in the private sector as well. It is best to check with your local retailer before you buy one in hopes of getting encrypted radios.